Method for producing a rimming ingot containing a fume-producing ingredient

ABSTRACT

FILL SUBSTANTIALLY ENTIRE BOTTLE-TOP INGOT MOLD, EXCEPT NECT, WITH MOLTEN RIMMING STEEL. ALLOW INGOT TO RIM WITHOUT RISING IN MOLD. ADD INGREDIENT CAPABLE OF FUMING (E.G., TELLURIUM) AFTER INGOT HAS RIMMED TO THE EXTENT DESIRED. POUR MOLTEN RIMMING STEEL INTO NECK OF MOLD IMMEDIATELY AFTER ADDING FUME-PRODUCING INGREDIENT. MECHANICALLY CAP INGOT, WITH BOTTOM OF CAPPING ELEMENT DIPPING INTO MOLTEN STEEL, IMMEDIATEDLY AFTER POURING STEP, TO SEAL INGOT AND PREVENT ESCAPE OF FUMES. FUME-PRODUCING INGREDIENT IS MIXED WITH INGOT&#39;&#39;S MOLTEN INTERIOR WHILE FUMING IS MINIMIZED. INGOT HAS RIM FREE OF FUME-PRODUCING INGREDIENT.

United States ?atent O METHOD FOR PRODUCING A RIMMING INGOT CONTAINING A FUME-PRODUCING INGREDIENT Robert N. Edmondson, Chesterton, and Kurt R. Mattson, Crown Point, Ind., assignors to Inland Steel Company, Chicago, Ill.

Filed Mar. 12, 1970, Ser. No. 18,953 Int. Cl. B22d 27/20 US. Cl. 164-57 8 Claims ABSTRACT OF THE DISCLOSURE Fill substantially entire bottle-top ingot mold, except neck, with molten rimming steel. Allow ingot to rim without rising in mold. Add ingredient capable of fuming (e.g., tellurium) after ingot has rimmed to the extent desired. Pour molten rimming steel into neck of mold immediately after adding fume-producing ingredient. Mechanically cap ingot, with bottom of capping element dipping into molten steel, immediately after pouring step, to seal ingot and prevent escape of fumes. Fume-producing ingredient is mixed with ingots molten interior while fuming is minimized. Ingot has rim free of fume-producing ingredient.

BACKGROUND OF THE INVENTION The present invention relates generally to methods for producing ingots from molten steel and more particularly to a method for producing a rimming ingot containing a fume-producing ingredient such as tellurium, selenium, sulfur or bismuth.

To produce a rimming ingot, an open-top ingot mold is filled with molten steel containing relatively little deoxidizing agent. Carbon monoxide is generated within the ingots molten interior and efiervesces through the top of the ingot, thereby maintaining the ingot top molten. As the rimming ingot freezes inwardly from the walls of the ingot mold, the solidified skin or rim of the ingot is relatively free of carbon and of many metalloids and is relatively pure iron.

Rimming can be stopped by putting a steel plate on the open top of the ingot mold, in contact with the molten surface of the ingot, and pouring large amounts of cooling water on the capping plate to solidify a crust on the top of the ingot. This stops the evolution of gas from the top of the ingot, in turn stopping the rimming action.

It is sometimes desirable to add, to a rimming ingot, an alloying ingredient which unavoidably produces undesirable fumes. Typical of such ingredients are tellurium, selenium, sulfur and bismuth. For example, to produce an extrudable, machinable steel, tellurium is added to a rimming steel ingot, in the ingot mold, after the steel has undergone some rimming. RAH extrudable, machinable steel and a method for producing it, using open-top molds and conventional rimming practice, are disclosed in Levy et al. application Ser. No. 802,798 filed Feb. 27, 1969.

When fume-producing ingredients are added to an ingot mold after it has been filled with rimming steel, and the rimming action is then stopped by the conventional procedure of using a capping plate (dscribed above), there is a substantial delay between the addition of the fume-producing ingredient and the formation of a solid crust over the top of the rimming ingot. This delay exposes workmen in the area to a substantial amount of undesirable fumes which are a health and safety hazard. Moreover, even with a capping plate, the steel may erupt at the ingot top causing delayed rimming; and this tends to concentrate the adition ingredient to a higher degree within the molten interior of the ingot than desired. Such a concentration requires discarding a larger amount of steel from the top of the ingot than would normally occur, thus reducing yield.

Another technique for stopping the rimming action utilizes a bottle-top ingot mold. As the name implies, the top of this ingot mold is substantially closed and has an internal neck of reduced cross section open at the top.

Conventional procedure utilizing a bottle-top ingot mold is to fill the ingot mold up to the neck of the mold, with the deoxidizing content of the molten steel adjusted so that, although carbon monoxide gas is formed within the molten interior of the ingot, evolution of the gas from the top surface of the molten steel, at the neck of the mold, is at a slower rate than formation of the gas. Accordingly, the volume of the molten steel increases, due to the relative retention of the gas, causing the molten steel to rise in the neck of the bottle-top ingot mold. A capping element is placed at the top of the neck, and when the rising molten steel contacts the bottom surface of the capping element, the steel freezes, thereby forming a solid seal at the top of the ingot mold neck; and this eventually stops the riming action.

It is undesirable to use the procedure described in the preceding paragraph when adding fume-producing ingredients. This is because, even if the ingredient were added immediately after the molten steel is poured into the ingot mold, there would still be a delay between the time the ingredient was added and the time the rising molten steel solidified against the bottom of the capping element; and the length of this delay cannot be readily controlled. All during this delay, undesirable fumes would escape through the top of the ingot mold neck because the capping element does not provide a gas-tight seal. A further disadvantage, in rimming steels to which telurium has been added to improve the machinability, is that many deoxidizing elements (e.g., aluminum, silicon, titanium), added to control gas formation in the ingot, form compounds in the steel which impair the machinability thereof.

Another technique utilizing the bottle-top ingot mold is to fill the entire ingot mold, including a Substantial amount of the neck, with molten rimming steel, and then place a capping element atop the neck with the bottom of the capping element extending into the molten steel in the mold neck (e.g., Belding U.S. Pat. No. 2,190,393). This causes the molten steel in the neck to freeze against the capping element, thereby sealing the ingot, and stop ping the rimming action.

It would be undesirable to use the last described method when adding a fume-producing element (such as tellurium), because adding the latter atop molten steel in the neck of the mold causes dangerous metallic sparks to fly out the top of the ingot mold; and this would be a health and safety hazard.

SUMMARY OF THE INVENTION In accordance with the present invention, a molten rimming steel, without the fume-producing ingredient, is poured into a bottle-top ingot mold, to substantially fill the mold while leaving substantially the entire mold neck empty. The ingot is then permitted to rim to the extent desired. Then, the fume-producing ingredient (e.g., tellurium, selenium, sulfur, bismuth) is introduced into the rimming molten steel within the ingot mold. Immediately thereafter, additional molten rimming steel is poured into the ingot mold, to fill at least a substantial part of the neck of the mold and form an ingot neck.

Immediately after the step of pouring the additional molten rimming steel into the ingot mold, the ingot is mechanically capped by placing a capping element atop the ingot mold and dipping the bottom of the capping element into the molten steel contained within the ingot neck to freeze the top of the ingot neck. This seals the ingot, stops the rimming action and prevents the escape of fumes.

As used herein, the term immediately means without intentional delay.

Machinability-impairing deoxidizing agents, such as aluminum, silicon or titanium, are excluded from the molten steel and from the ingot mold.

In one embodiment, the fume-producing ingredient may be added to the ingot mold together with the additional molten rimming steel.

Other features and advantages are inherent in the method claimed and disclosed or will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view of a bottle-top ingot mold, used in an embodiment of a method in accordance with the present invention, showing the capping element removed;

FIG. 2 is a vertical sectional view, similar to FIG. 1, but with the capping element in place.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the figures, a bottle-top ingot mold is indicated generally at and includes side walls 11, a top 12 and an internal neck 13.

Molten rimming steel is introduced into the interior of mold 10 and permitted to rim to the extent desired. The molten rimming steel may have the following typical composition, in wt. percent:

Carbon 0.03-0.15 Manganese 0.254160 Sulfur 0.025 maximum Phosphorus 0.015 maximum Iron Balance Ingot mold 10 is filled with molten rimming steel to about the level indicated by dash-dot line 15. Between 95 and 100% of the volume of the mold, minus mold neck 13, is filled during the first pouring step. Neck 13 is intentionally left empty.

Because a molten rimming steel is substantially devoid of deoxidizing agents, carbon reacts with oxygen in the molten rimming steel to form carbon monoxide gas. The gas eifervesces upwardly through molten steel surface and passes outwardly from the ingot mold through neck 13. The rate at which carbon monoxide gas leaves the molten interior 14 of the ingot is approximately the same rate as carbon monoxide is formed. Therefore there is not significant increase in the volume of molten steel 14, and the molten steel does not rise significantly above level 15 into the neck of the mold. As carbon monoxide is formed, a skin 16 solidifies adjacent side walls 11 of the ingot mold. This skin or rim 1 6 is devoid of carbon and is relatively pure iron.

After the steel has rimmed to the extent desired, the addition ingredient (e.g., tellurium) is introduced into the molten steel through neck 13 of the ingot mold. Because of the molten steels top surface 15 is no higher than the bottom of mold neck 13, there is relatively little metallic sparking outwardly through the top of neck 13 compared to What would occur if neck 13 was substantially full of molten steel at the time the addition ingredient was added.

The addition ingredient is mixed within molten interior 14 by convection currents inherent in the molten interior of a solidifying ingot and by the turbulence produced by the formation of carbon monoxide gas within molten interior 14.

Immediately after adding the addition ingredient. additional molten rimming steel is poured into the neck of mold 10 to approximately level 17. Immediately after the second pouring step, the ingot is mechanically capped by 4 placing a capping element 20 atop ingot mold 10 and dipping the bottom 21 of the capping element into the molten steel within the ingot neck to freeze the top of the ingot neck, as indicated at 22 in FIG. 2. This seals the ingot thereby preventing the escape of fumes from the ingot.

Because the second pouring step and the capping step are successively performed without intentional delay after the fuming ingredient is added, escape of fumes from the ingot is minimized. After capping, carbon monoxide continues to form within molten interior 14 until the partial pressure of the carbon monoxide gas increases to the pressure of the mechanical cap and of the solidified steel 22 beneath the cap. Mixing continues while fuming has ceased.

No significant amounts of deoxidizing agents (aluminum, silicon, titanium, for example) are added to the molten steel or to the ingot mold. Not only does this prevent the steel from rising in the neck of the ingot mold, but, also, it enhances the machinability of steel produced from the ingot because the deoxidizing agents can form machinability-impairing compounds within the steel (e.g., aluminates, silicates, titanates).

In another embodiment, the addition ingredient (e.g., tellurium) and the additional molten rimming steel for filling mold neck 13 to level 17 may be added simultaneously, after molten steel 14 has rimmed to the extent de sired. In this embodiment, all of the other steps are essentially the same as in the previously described embodiment.

After the ingot has solidified, it may be rolled into a steel bar, or the like, and the resulting product has a skin devoid of carbon and of the addition ingredient and an interior containing the addition ingredient. Thus, for example, if the addition ingredient is tellnrium, the skin of the bar would be devoid of tellurium, but the interior of the bar would contain tellurium. The bar would be machinable due to the inclusion of tellurium and the exclusion of machinability-impairing deoxidizing ingredients. Moreover, because the skin of the bar is devoid of carbon, the bar would be readily extrudable.

What is claimed is:

1. A method for producing a rimming ingot containing an ingredient capable of producing undesirable fumes, said method comprising the steps of:

pouring a molten rimming steel without said inegrident into a bottle-top ingot mold and substantially filling said mold while leaving substantially the entire neck of said mold empty;

permitting said ingot to rim Without a rise in the level of molten steel in the ingot mold;

introducing said ingredient into the molten steel within said ingot mold, after said ingot has rimmed to the extent desired;

pouring additional molten rimming steel into said ingot mold, to fill at least a substantial part of the neck of said mold and form an ingot neck, no later than immediately after adding said ingredient;

and then mechanically capping said ingot by placing a capping element atop said ingot mold and dipping the bottom of said capping element into the molten steel within the ingot neck to freeze the top of the ingot neck, thereby sealing the ingot;

said capping step being performed without intentional delay after said last recited pouring step.

2. A method as recited in claim 1 wherein:

said ingredient is introduced into the ingot mold simultaneously with the pouring of said additional molten rimming steel.

3. A method as recited in claim 1 wherein:

said additional molten rimming steel is poured into the ingot mold without intentional delay after said ingredient-introducing step.

4. A method as recited in claim 1 wherein:

-100% of the volume of said mold, minus the mold 6 neck, is filled during said first recited pouring step. 5. A method as recited in claim 1 wherein: References Cited said ingredient improves the machinability of the steel: UNITED STATES PATENTS said method comprising the further step of excluding machinability-impairing deoxidizing agents from said 5 2,108,254 2/1938 Devafley 75-45 molten steel and from said ingot mold. 211431410 1/1939 Domm 6. A method as recited in claim 1 wherein said in- 2,236,504 4/1941 Hfirty 75-45 gredient comprises one or more of tellurium, selenium, 2,854,329 9/1958 Rossborough 16457 sulfur and bismuflm P0016 7. A method for producing an ingot of extrudable, ma- 1O chinable steel in accordance with the method of claim 1 SPENCER OVERHOLSER Primary Examiner wherein said ingredient is tellurium. J. S. BROWN, Assistant Examiner 8. A method as recited in claim 7 and comprising: excluding machinability-impairing deoxidizing agents U.S. C1. X.R.

from said molten steel and from said ingot mold. 15 7556 

